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We demonstrate Josephson junction based double-balanced mixer and phase shifter circuits operating at 6-10 GHz, and integrate these components to implement both a monolithic amplitude/phase vector modulator and a quadrature mixer. The devices are actuated by flux signals, dissipate no power on chip, exhibit input saturation powers in excess of 1 nW, and provide cryogenic microwave modulation solutions for integrated control of superconducting qubits., Comment: accepted version

We have studied the statistics of plastic rearrangement events in a simulated amorphous solid at T=0. Events are characterized by the energy release and the ``slip volume'', the product of plastic strain and system volume. Their distributions for a given system size $L$ appear to be exponential, but a characteristic event size cannot be inferred, because the mean values of these quantities increase as $L^{\alpha}$ with $\alpha \sim 3/2$. In contrast to results obtained in 2D models, we do not see simply connected avalanches. The exponent suggests a fractal shape of the avalanches, which is also evidenced by the mean fractal dimension and participation ratio., Comment: Accepted for publication in Physical Review Letters

In seeking to understand at a microscopic level the response of dislocations to stress we have undertaken to study as completely as possible the simplest case: a single dislocation in a two dimensional crystal. The intention is that results from this study will be used as input parameters in larger length scale simulations involving many defects. We present atomistic simulations of defect motion in a two-dimensional material consisting of atoms interacting through a modified Lennard-Jones potential. We focus on the regime where the shear stress is smaller than its critical value, where there is a finite energy barrier for the dislocation to hop one lattice spacing. In this regime motion of the dislocation will occur as single hops through thermal activation over the barrier. Accurate knowledge of the barrier height is crucial for obtaining the rates of such processes. We have calculated the energy barrier as a function of two components of the stress tensor in a small system, and have obtained good fits to a functional form with only a few adjustable parameters., Comment: 6 pages, 4 figures Submitted to Proceedings of MRS Fall 1999 meeting, Symposium A

An edited record of the conversions between the Apollo 12 astronauts and mission control pertaining to the geology of the landing site, is presented. All discussions and observations documenting the lunar landscape, its geologic characteristics, the rocks and soils collected and the lunar surface photographic record are included along with supplementary remarks essential to the continuity of events during the mission.

The Apollo 15 lunar module (LM) landed on the mare surface of Palus Putredinis on the eastern edge of the Imbrium Basin. The site is between the Apennine Mountain front and Hadley Rille. The objectives of the mission, in order of decreasing priority, were description and sampling of three major geologic features-the Apennine Front, Hadley Rille, and the mare. The greater number of periods of extravehicular activity (EVA) and the mobility provided by the lunar roving vehicle (ROVER) allowed much more geologic information to be obtained from a much larger area than those explored by previous Apollo crews. A total of 5 hours was spent at traverse station stops, and the astronauts transmitted excellent descriptions of the lunar surface while in transit between stations.

The well-developed systems of lineaments that suggest regional fracturing or layering of the bedrock in the mountains at the Apollo 15 site may be illusions created by oblique lighting rather than expressions of true geologic structure. Supporting evidence includes: (1) occurrence of similar dominant lineament trends on many of the slopes even though the slope orientations differ widely; (2) presence of a thick mantling regolith that should conceal bedrock structures; (3) approximate symmetry of some of the lineament sets about the sun line; (4) lack of clear-cut topographic expression for many of the lineaments; and (5) general similarity of the lunar lineaments to lineament patterns produced by low oblique lighting on model surfaces mantled by fine sifted powder. Locally, as at Silver Spur, some lineament trends are related to distinct topographic features and are more confidently interpreted to reflect underlying geologic structures.

Locations of documented samples returned by Apollo 15 including photographs of sample sites, crew descriptions, general rock types, and numbering systems

Fluoroplanigraphic system for rapid presentation of single plane body sections with reduced X ray exposure to patients

Lunar geology based on Apollo 14 photographs and soil and rock samples

Experimental studies have indicated that: (1) The response of digitized fluoroscopic imaging systems is linear systems is linear with contrast over a rather wide range of absorber and cavity thicknesses. (2) Contrast changes associated with the addition of aluminum, iodine containing contrast agents and air of thicknesses 1mm or less can be detected with a 95% confidence level. (3) The standard deviation associated with such determination using clinically available X-ray generators and video disc recording is less than 1 percent. A large flat screen X-ray image intensifier has been constructed and some preliminary results obtained. Sensitivity achieved makes dose reduction a factor often greater than previously reported for a system using a conventional X-ray image intensifier.